Proof: If \(M\)  is not projective or the Picard number of \(M\)  is less than four, apply REF 
to get a projective deformation \(M^{\prime }\)  with Picard number at least four such that
all MBM classes of type \((1,1)\)  on \(M\)  remain of type \((1,1)\)  on \(M^{\prime }\) . Then use the deformation invariance of
MBM property proved in [1]} to conclude that these MBM classes remain MBM on \(M^{\prime }\)  and therefore the primitive
ones must have bounded square by the preceding theorem.
